Simplify date parsing (#195)

Create common functions parse_date, parse_month_year_date and parse_datetime.

Those functions support trying multiple formats, and come with default formats lists that support most of the date format encountered so far.

Notable change: year-month dates are now set to the end of month (impacted couchbase-server and ibm-aix).

src/common/dates.py

@@ -0,0 +1,51 @@
+from datetime import datetime, timezone
+import calendar
+
+
+def parse_date(text, formats=frozenset([
+    "%B %d, %Y",  # January 1, 2020
+    "%b %d, %Y",  # Jan 1, 2020
+    "%B %d %Y",   # January 1 2020
+    "%b %d %Y",   # Jan 1 2020
+    "%d %B %Y",   # 1 January 2020
+    "%d %b %Y",   # 1 Jan 2020
+    "%d-%b-%Y",   # 1-Jan-2020
+    "%d-%B-%Y",   # 1-January-2020
+])) -> datetime:
+    """Parse a given text representing a date using a list of formats.
+    """
+    return parse_datetime(text, formats, to_utc=False)
+
+
+def parse_month_year_date(text, formats=frozenset([
+    "%B %Y",      # January 2020
+    "%b %Y",      # Jan 2020
+    ])) -> datetime:
+    """Parse a given text representing a partial date using a list of formats,
+    adjusting it to the last day of the month.
+    """
+    date = parse_datetime(text, formats, to_utc=False)
+    _, last_day = calendar.monthrange(date.year, date.month)
+    return date.replace(day=last_day)
+
+
+def parse_datetime(text, formats=frozenset([
+    "%Y-%m-%d %H:%M:%S",         # 2023-05-01 08:32:34
+    "%Y-%m-%dT%H:%M:%S",         # 2023-05-01T08:32:34
+    "%Y-%m-%d %H:%M:%S %z",      # 2023-05-01 08:32:34 +0900
+    "%a, %d %b %Y %H:%M:%S %Z",  # Wed, 01 Jan 2020 00:00:00 GMT
+    "%Y-%m-%dT%H:%M:%S%z",       # 2023-05-01T08:32:34+0900
+]), to_utc=True) -> datetime:
+    """Parse a given text representing a datetime using a list of formats,
+    optionally converting it to UTC.
+    """
+    text = text.strip()
+    for fmt in formats:
+        try:
+            date = datetime.strptime(text, fmt)
+            date = date.astimezone(timezone.utc) if to_utc else date
+            return date
+        except ValueError:
+            pass
+
+    raise ValueError(f"'{text}' could not be parsed as a date with any of the formats: {str(formats)}")